A: For several reasons I think, the first being a policy of non-promotion that was pervasive from the time of publication in 1955 until the 1990s when the internet took hold.
Many of the early readers thought the book should only be spread through word of mouth, from person to person. The book itself is another reason--it's written in a style that speaks to introspective and thinking people and not particularly to the general reading public. General readers prefer their inspiration coated in fluff that's easy to digest and The Urantia Book is unequivocal in relating its message. And another reason may be that The Urantia Book is a personal—not a group—revelation; it's written for the person holding it on their lap, reading its words--that's about the only way the revelation is disclosed and transmitted... from the ink on the page to the mind of the reader. I can fill the mind of someone else with all the cool, unique, fascinating facts the book contains and it just becomes a bunch of interesting stuff. I can't transmit the revelatory nature of its message. That only comes from putting in the time and effort required to read the book for oneself. Lots of people think they know all about The Urantia Book but unless they've actually read it for themselves they really don't.
We all wish for peace and tranquility here--but wishing accomplishes nothing. The Urantia Book makes it clear that the only way true peace and tranquility will come is through the teachings of Jesus infusing the hearts and minds of the world's inhabitants. To do that the true teachings of Jesus need to be removed from the hold on them that Christianity imposes-to be freed for all religions and all people saparate from religious dogma.
We have a study titled "War and Peace" in the Spiritual Studies category... you can go to it here... that condenses the teachings of The Urantia Book on this topic, discussing the value and tragedy of war and how to get past it; it may be of some help to you."